This invention relates to a walking beam furnace for heating metallurgic materials such as billets, bars, blooms and the like, having different temperatures of introduction into the furnace and/or different cross sections, particularly different thicknesses and/or different characteristics, and/or being distinguished from one another by any other characteristic requiring different heating time.
The higher quality of the steel products obtained by a continuous casting process permits to omit, in many cases, any inspection of the cast materials, which inspection requires the cooling of said materials to temperatures approaching the ambient temperature. This simplification, inter alia, ensures the advantage from the standpoint of energy saving, to load into the heating and balancing furnaces materials which are still hot as coming from the continuous casting operation. This advantage of introducing high-temperature materials is not possible in the known walking beam furnaces, since the latter are intended to receive a charge comprising materials at approximately the same temperature. In fact, should some articles be introduced at temperatures considerably different from the average temperature, they would be discharged from the furnace at a temperature lower than that required for the rolling operation, or they would be overheated or partially molten. In order to avoid this drawback as much as possible, the operation of the rolling mill downstream of the walking beam heating furnace must be timed with the operation of the continuous casting process, so that the heated materials reach the furnace without effecting dwells of variable duration, thus avoiding any different degree of cooling of the materials.
However, practically, this requirement gives rise to some difficulties, particularly in the installations comprising one single continuous casting apparatus and one signal rolling mill line. To avoid said difficulties, in order to obtain a uniform temperature of the heated articles at the outlet of the walking beam furnace, it is even preferred a complete cooling of all the articles coming from the continuous casting, thus losing the advantages of introducing the articles into the furnace in a hot condition.
This invention aims to avoid said drawbacks and its object is to provide a heating method, in combination with walking beam furnaces, permitting to introduce into a furnace series of articles (billets, bars, blooms) having temperatures and/or cross sections, particularly thicknesses and/or characteristics considerably different from one another, and yet to obtain at the outlet of the furnace articles having a temperature which is substantially the same and is suitable for rolling mill action. The method of the invention, therefore, permits an elastic association between the hot rolling mill downstream of the walking beam furnace and the apparatus upstream of said furnace.
The method of the invention substantially comprises the steps of feeding the materials to be heated, at least partially, along the outer side of the furnace in the same direction as the materials within the furnace and of introducing them laterally into said furnace at different and varying positions as a function of their temperature and/or cross-section, particularly their thickness and/or quality and/or any other characteristic. Under another aspect of the invention, in combination with the above method or as an alternative thereto, the heated materials are discharged laterally from the furnace at different and varying positions when they reach the desired discharge temperature, and the discharged materials are then advanced along the outer side of the furnace in the same direction as the materials within the furnace.
To carry this method into effect, the invention provides a walking beam furnace, substantially characterized in that it comprises a plurality of successive inlet or introduction doors and a plurality of successive outlet or discharge doors, and, on at least one side portion of the furnace, adjacent and longitudinally thereto, in register with the introduction and/or discharge doors, it comprises an external conveyor for the materials (billets, blooms, bars) which is timed with the walking beam conveyor within the furnace and is adapted to advance the materials in the same direction and at the same speed as the walking beam internal conveyor, means being provided to introduce the materials from the external conveyor into the furnace through any of the side introduction doors onto the walking beam internal conveyor, and/or discharge the materials through any of the side discharge doors onto said external conveyor, and detection and control means being provided to select--as a function of the temperature and/or thickness, and/or quality--the oncoming materials to be heated and to introduce them directly into the furnace through the first introduction door or to send them onto the corresponding external conveyor and introduce them with a longer or shorter delay through one of the successive side introduction doors in register with an unoccupied place on the internal walking beam conveyor, and/or to select the heated articles and discharge them through the last discharge door or with a longer or shorter advance through one of the preceding side discharge doors, onto the corresponding external conveyor.
The walking beam furnace with external timed conveyor according to the invention can be constructed in several ways. Thus, for example, the external conveyor associated to a plurality of successive doors can be provided only at the inlet side or at the outlet side, or both at the inlet and outlet sides. The succession of inlet or outlet doors can be so constructed as to allow the passage of one article at a time, or otherwise they can be wide enough to permit each the introduction and/or discharge of one article at different positions along the furnace. If desired, one single side inlet and/or outlet door could be provided extending along the entire length of the respective external conveyor.
The external conveyor and the inlet or outlet means associated therewith can be constructed in various ways. In a preferred embodiment, the external conveyor comprises a step-by-step conveyor, preferably a walking beam conveyor similar to the internal walking beam conveyor. The means to introduce the materials into the furnace from the external side conveyor and/or to discharge the materials onto the external side conveyor can comprise one or more axial load pushers.
If desired, in proximity of the side external inlet or outlet conveyor, a suitable heating means can be provided for the materials being conveyed on said external conveyor, for example to avoid or to minimize the cooling of these materials and/or to effect a pre-heating thereof. For this purpose, according to the invention, the side external conveyor (or conveyors) can be enclosed within respective chambers, preferably insulated and suitably heated, for example, by the exhaust gases of the walking beam furnace.